Separation of copper from zinc



Patented Nov. 7, 1944 2 "SEPARKTION or corrsn FROM ZINC John 0. Bay, Cleveland Heights, Ohio, assignor to The Harshaw Chemical Company, Elyria,

Ohio, a corporation of Ohio No Drawing. Origi al application March 23,

1942, Serial No. 43 ,915. Divided and this application September 20, 1943, Serial No. 503,153

1 Claims. (C1. 23135) I in the solution initially, and

This invention relates to the separation of copper from alloys or other 'mixtures'of the same with one or'more metals electropositive to copper. separation of copper from scrap alloys or other mixtures containing copper, such as for example, copper-nickel scrap (e. g. Monel, Nickeline, Constantan, etc.) and is applicable to alloys or other mixtures of copper with, among other metals electropositive to copper, aluminum, manganese, beryllium, zinc, iron, cadmium, cobalt, nickel, antimony and tin. The alloy may contain copper and any one or more of the other metals named. It may also contain, in addition to the above metals, minor amounts oielements not electropositive, to copper, which, providing the alloy as a whole is electropositive, do not affect the basic reactions. However, such elements may, because of the insolubillty of their compounds or the formation of inert coatings on the metal, eventually inhibit the reaction unless'special means, dififering with the circumstances, are used to prevent such iormation. These special means affect only those elementsiifthe alloy which are not electropositive to copper and, therefore, do not aflect the general procedure which constitutes thisfinvention.

I have discovered that if a reaction mixture comprising a body of an alloy or other mixture of the class stated, an aqueous acid solution contaming ions of the class consisting of chloride More specifically, the invention relates to and sulfate or both and finely divided sulfur is heated, the copper content of the alloy or other mixture, together with the copper in solution, if

any, is convertedjso coppersulfide while themore electropositive metal or 'metais go into solution to form their salt or salts, sulfur and free acid in the solution being used up in the reaction. Not only does the free acid in the solution combine, with the more .electropositive metal or metals, the negative ion released by reaction of the copper salt in the solution with sulfur to form copper sulnegative ions for the reaction with the more elec- 5 tropositive metal or metals.

Disregarding side reactions, which in some instances cause loss of sulfur as hydrogen sulfide the severe; factors can be approximately balanced, thus, the amount of sulfur can be approxibut 40 imetal wouldbe present at all the copper to be released from the alloy as the more electropositive constituents dissolve. The amount of free acid can be such that its negative'ion plus the negative ion associated with copper initially in solution will be approximately such as required to dissolve the electropositive metal. The amount.

of alloy or other mixture of metals theoretically required to remove all copper from solution is such as to supply to the solution electropositive metal or metals in quantity molecularly equivalent to the compounds furnishing the negative ions'in the solution.

Since, practically, the composition of the alloy will always be known, the other factors can be calculated in advance so that at the end of the reaction there will be left in the reaction vessel only a copper free solution of the salt or salts of the electropositive metal or metals and a dense and easily filterable' precipitate of copper sulfide.

This balance may be preferred practice, but as shown by some of the examples, considerable deviation from a balance does not interfere with the reactions and may be considered satisfactory practice. For instance, if the metals are in the form of powder or very finely divided, or as thin scrap or fine wire, a balance as above would probably be preferred. 'However, if the metals are in the form of coarse or heavy scrap,.a countercurrent process might be preferred in which excess the end oi each batch,"

thismethod shortening the reaction time by making available a larger amount of metallic surface. One of the advantages of the method is that the copper sulfide does not adhere to the excess metal so that during the reaction the metal surfaces are always relatively clean and reactive, and at the conclusion ofthe reaction, the excess metal may be readily separated from the copper sulfide precipitate. The remaining metal has essentially the composition of the original metal, being neither substantially enriched by copper nor substantially depleted of the more electropositive a considerable proportion of the negative ion, in

fact, as hereinafter explained, if no copper salt is in solution initially the acid can furnish the entire amount of negative ion.

In the practical operation of the process, there are some slight divergencesfrom theoretical results but they are not of great importance. For example, some metal and some, free sulfur are mately such as required to react with all copper frequently found in the, precipitate and the com- .insoluble salt.

While I prefer to employ finelygroundor flowposition of the copper sulfide itself may vary between cupric sulfide and cuprous sulfide.

While the result is the same in each case the chemical reactions involved seem to be several, the importance of each of which varies accord ing to the acid and metal employed. When metals highly electropositive to copper are employed, more or less metallic copper is thrown out first, this then reacting with sulfur to form copper sulfide. If copper is thrown out as an adherent coating, the rate at which it is thrown out will be increasingly slower until the sulfur has combined with it when the two reactions seem to proceed at a balanced rate. When the metal is not so greatly electropositive, the combination of sulfur and copper may take place at the surface ofthe metal without visible evidence of intermediate stages. If copper'is present in the solution at the start and is in the form of the chloride, there may be reduction first followed by the formation of the sulfide at some distance from the metal surface. However, if cupric sulfate is present in a wholly sulfate solution, the same formation of sulfide still occurs. There is frequently more or less formation of hydrogen sulfide, the amount being, apparently, somewhat dependent upon themetal employed and upon the rate of addition of the sulfur to the solution. The precipitation of copper by Has, at least to some extent, seems likely. v

The process, asdescribed thus far, presupposes that the initial reaction mixture contains in solution salts of the constituent metals of the alloy. This is not essential. If the initial mixture contains merely the alloy, water, sulfur, and acid, the copper from the alloy will react with the sulfur while the more electropositive metal or metals will dissolve. After a short interval of operation, the reaction mixture will contain all the components as in the previously described batch, except that there will be at no time any considerable concentration of copper in solution.

It is, then, clear that copper in solution is not """rmsmemoaisappli per and more electropositive mtalswhicn are not alloys. Examples of such use would be the separation of a mixture of metallic powders or finely disseminated metals in a non-metallic matrix such as might be obtained by in situ or gaseous reduction of an ore, one of the powdered metals or disseminated metals being copper, and the others more electropositive. By heatin such a. mixture of metals with acid (or a suitable metallic salt), water, and sulfur so that the copper is precipitated as copper sulfide and the more electropositive metals are put into solution, the essentials of this invention in its broad aspect have been complied with.

The negative ions preferred are the chloride ion, the sulfate ion, or a mixture of the two, but I may make use of other negative ions which do not exert a solvent action on copper sulfide and which do not precipitate the other metal as an era of sulfur, the sulfurneed not be in this form.

. I have also used other formsof sulfur including small lumps or as when the boiling point of sulfur, the latter is used as an emulsion of melted sulfur. I have also added in many cases a small amount of wetting agent to prevent agglomeration and floating of theflnely powdered sulfur. This is not necessary, nor is there any catalytic effect to be gained by the wetting agent. The reaction proceeds without this addition, and with proper mixing of the sulfur in a. small portion of acid or acid and strong salt solution its wetting may be accomplished.

A typical. utilization of the process would be in'the treatment of a copper-zinc scrap. This scrap can be dissolved to form a'mixed, concentrated solution of, for example, the chlorides of zinc and copper. This can be done by known methods which form no part of the present invention. This concentrated solution of the chlorides can then be heated with more of the scrap and elemental sulfur during which the copper can be completely removed as the sulfide and replaced by zinc so that the solution becomes copper free and correspondingly more concentrated with respect to zinc.

This application is a division of my co-pending application, Serial No. 435,915, filed March 23, 1942. a

The following specific example will serve to illustrate the invention:

Example The initial solution contained 143 g. of Zn and 4.5 g. of On both as chlorides, 100 cc. of water and 40 cc. of 18 B. I-ICl. To this was added 27.2 g. of strip brass and 7.0 g. of sulfur. The whole was heated to boiling at which point the sulfur was melted and in the form of small droplets throughout the solution. After about 1 to 2 hours during which there was evolution of H28, 6.4 g; of the alloy haddisintegrated with the precipitation of 10.5 g. of copper sulfide. The solution was copper free, the precipitate essentially free of zinc and the remaining brass,

- while in this case having a thin surface film of copper enrichment, had a. still reactive surface. Other experiments on brass indicate that the surface enrichment by copmr is not always present.

.Having thus described my claim is:

1. A process for obtaining copper sulfide and a zinc salt from a zinc-copper alloy which coinprises heating an aqueous, acid solution containing a copper salt and a zinc salt in contact with the alloy and elemental sulfur.

2. A process for obtaining copper sulfide and zinc chloride from a zinc-copper alloy which comprises heating an aqueous, acid solution containing zinc chloride and copper chloride in coninvention, what I tact with the alloy and elemental sulfur.

zinc chloride from a zinc-copper alloy which comprises heating at its boiling point an aqueous, acid solution containing copper chloride and zinc chloride in contact with thealloy and finely divided elemental sulfur.

JOHN O. HAY. 

